The present invention relates to techniques for controlling a polarizing filter and, more particularly, to a method and device for automatically controlling a polarizing filter. The method and device feature automatically sensing, measuring, and analyzing at least one parameter associated with direction of a polarizing filter by an electronic direction/motion sensing mechanism, receiving a signal from the electronic direction/motion sensing mechanism relating to the at least one parameter associated with direction of the polarizing filter by a rotation control circuit, and receiving a signal from the rotation control circuit relating to the at least one parameter associated with direction of the polarizing filter by a polarizing filter rotating mechanism for automatically rotating the polarizing filter.
Basic principles and details relating to propagating electromagnetic radiation and to polarization of propagating electromagnetic radiation needed for properly understanding the present invention are provided herein. Complete theoretical descriptions, details, explanations, examples, and applications of these and related subjects and phenomena are readily available in standard references in the fields of physics, materials science, optics, photography, and photographic equipment. The present invention is primarily directed to applications of a polarizing filter in the field of photography, however, the present invention clearly can be directed to applications of a polarizing filter in a variety of other fields involving the use of polarized electromagnetic radiation for viewing, imaging and/or projecting through short or long distances, for example, involving the use of a microscope, binoculars, a telescope, or a laser beam device.
Electromagnetic radiation which is unaffected and untreated by external influences, in general, and unpolarized, in particular, such as that of unpolarized light or any other radiation, behaves as a propagating transverse wave vibrating equally and randomly in all directions perpendicular to the direction of propagation. Polarization is generally denoted as the uniform and nonrandom elliptical, circular, or, linear or planar, variation of the vibrational orientation of the wave motion of such electromagnetic radiation. Linear or plane polarized electromagnetic radiation occurs when all the vibrating electromagnetic field components of the propagating electromagnetic radiation are oriented in the same direction. A simple way of describing this phenomenon is by considering the wave motion of electromagnetic radiation as a vector sum of two such vibrations in perpendicular planes, vibrating perpendicular to the direction of propagation, whereby linear or plane polarized electromagnetic radiation results when one of the two components is partly or entirely removed from the propagating wave motion of the electromagnetic radiation.
Sources of unpolarized electromagnetic radiation can be naturally existing, such as the sun or the moon, or, can be man made, such as a manufactured electromagnetic radiation source, for example, a device generating a highly focused or coherent beam of electromagnetic radiation, such as a laser beam, or, a device generating spread out or diffuse electromagnetic radiation, such as an incandescent lamp, a fluorescent lamp, an infra-red lamp, an ultra-violet lamp, or, a device generating a combination of focused and diffuse electromagnetic radiation, such as a photographic flash lamp, spot light, or flood light. Unpolarized electromagnetic radiation can be linearly or plane polarized by any of various linear or plane polarizing mechanisms, the most well known and characterized being absorption, scattering, or reflection, each of which is basically described herein.
In the linear or plane polarizing mechanism involving absorption, unpolarized propagating electromagnetic radiation, originating from a natural source or a man made source, is directed into a medium having a unique structure which passes or transmits incident electromagnetic radiation polarized in one direction, commonly referred to as the xe2x80x98passing directionxe2x80x99, while strongly absorbing or xe2x80x98blockingxe2x80x99 electromagnetic radiation polarized in the perpendicular, or xe2x80x98blockingxe2x80x99, direction. Accordingly, such a linear or plane polarizing medium functions as a special type of filter, commonly referred to as a xe2x80x98polarizing filterxe2x80x99, for blocking or filtering out a selected part, or fraction, of the incident electromagnetic radiation. A single polarizing filter polarizes up to a maximum of half the intensity of unpolarized electromagnetic radiation, and, depending upon the relative angular orientation of the polarizing planes of two polarizing filters placed in series, transmission of electromagnetic radiation, initially unpolarized when directed into the first polarizing filter, successively passing through the second polarizing filter can be controlled down to a minimum of zero if the double polarization is complete, in accordance with the well known Malus cosine-squared law.
Different types of media, such as a polarizing prism, or, a polarizing sheet, which are widely used as polarizing filters, are known for producing absorption type of linear or plane polarization of electromagnetic radiation. A polarizing prism is made of a material, for example, calcite, whose crystal structure exhibits double refraction or birefringent characteristics, whereby the crystal structure has a different index of refraction for each direction or plane of polarization. Since electromagnetic radiation of one polarization is bent more strongly than the other, it is possible to separate the polarized components by total internal reflection, for example, by using a Nicol prism, or, a Glan-Thompson prism, or, by deviation in different directions, for example, by using a Rochon prism, or, a Wollaston prism. A polarizing sheet, for example, any one of the variety of different types of polarizing sheets manufactured by the Polaroid Corporation, USA, is made by aligning microscopic crystals of an appropriate material in a suitable base.
A special case of polarizing electromagnetic radiation is when linear or plane polarized electromagnetic radiation such as light traverses a crystal such as calcite perpendicular to its axis, the light is transformed into elliptically polarized, or, circularly polarized light.
In the field of physics, in general, and materials science, in particular, linear or plane polarizing media are used for producing a well defined and characterized source of polarized electromagnetic radiation, such as that produced by placing an appropriately designed and constructed polarizing filter in front of the beam of a source of electromagnetic radiation such as a laser device, for studying electronic structure, properties, and behavior of materials.
In the field of photography, propagating electromagnetic radiation in the form of scattered light, glare or intense light, and other strong reflections of light, often interfere with the photographic process and degrade photographs in many ways, for example, by diluting colors, by obscuring or distracting a photographer from important image details, or by forcing less than optimal exposure compromises. Fortunately, for photographers, such xe2x80x98interfering lightxe2x80x99 is associated with varying degrees of polarization, and this association provides a relatively easy way to eliminate, minimize, or, exploit, the xe2x80x98interfering lightxe2x80x99, by using a polarizing filter set at optimum or strategic polarizing angles, while capturing the remaining desired light required for the photographic process.
In the linear or plane polarizing mechanism involving scattering, unpolarized propagating electromagnetic radiation, originating from a natural source or a man made source, is directed into a medium which absorbs and re-radiates or scatters the incident electromagnetic radiation, such that the scattered electromagnetic radiation leaving the medium is strongly polarized in the direction perpendicular to the incident direction of propagation. Gas phase media, for example, the atmosphere containing gas molecules, water droplets, and other airborne particles, absorb and scatter electromagnetic radiation, and are known for producing scattering type of linear or plane polarization of electromagnetic radiation.
Of importance to photographers is that atmospheric scattering of sunlight is least at local noon in clean, dry air, resulting in a sharp deep blue color of the sky, whereas, late sunlight skimming the horizon loses much of its blue-green content to scatter along its long path through the lower atmosphere before reaching a viewer, resulting in red-yellow sunsets. Adding moisture or particulates to the atmosphere substantially increases scattering efficiency at longer, redder, wavelengths. With more colors represented in their scattered light, clouds look white, and hazy (damp or smoggy) skies take on a grayish to whitish cast. Accordingly, bright white scattered light directed into a camera effectively mutes or desaturates all the colors in a particular scene, especially the blue of the sky, whereas, bright blue scattered light effectively desaturates all other colors. Fortunately, scattered electromagnetic radiation, such as scattered light, is strongly polarized perpendicular to the incident direction of the unpolarized electromagnetic radiation propagating from a light source such as the sun, the moon, or, a photographic flash lamp, at all wavelengths. Here, the polarization mechanism of scattered light enables differentiating interfering scattered light from desirable and largely unpolarized light reflected from photographic subjects or objects.
In the linear or plane polarizing mechanism involving reflection, unpolarized propagating electromagnetic radiation, originating from a natural source or a man made source, is directed at an angle of incidence onto the surface of a medium which reflects or polarizes more of the incident electromagnetic radiation in the direction perpendicular to the plane of incidence, that is, parallel or tangential to the reflecting surface of the medium, than in the direction of the plane of incidence, and, refracts, by transmitting or absorbing, according to the physicochemical and optical properties of the medium, a fraction of the incident electromagnetic radiation into the medium in the plane perpendicular to the direction of reflection. Here, according to standard definitions, the angle of incidence is the angle between the path of the incident electromagnetic radiation and the normal or perpendicular to the reflecting surface at the point of reflection, the angle of reflection is the angle between the normal or perpendicular to the reflecting surface of the medium and the path of the reflected light at the point of reflection, and, the plane of incidence is the plane containing components of incident and reflected electromagnetic radiation and is always normal or perpendicular to the reflecting surface at least at the point of reflection.
At a certain angle of incidence, well known as Brewster""s angle, for such a reflecting medium, the reflected electromagnetic radiation is entirely polarized and reflected perpendicular to the plane of incidence, that is, parallel or tangential to the reflecting surface of the medium, because the component of the incident electromagnetic radiation ordinarily reflected in the direction of the plane of incidence is completely refracted into the medium. For photographic applications taking place in air, the Brewster""s angle of most such reflecting surfaces is approximately 55 degrees. At other angles of incidence, reflected light from the surfaces of such media is only partially polarized, but the net polarization remains tangential to the reflecting surface.
Non-metallic or dielectric media which feature a generally smooth or polished reflecting surface, such as a sheet or plate of glass, a clean or polished non-metallic table-top, water, a wet non-metallic surface, foliage, or, non-metallic car paint, are known for producing reflection type of linear or plane polarization of electromagnetic radiation. Reflections from such types of surfaces are also commonly referred to as specular reflections. Unpolarized electromagnetic radiation reflected by smooth metallic surfaces, or, reflected by rough surfaces such as rocks, trees, animals, or dirt, essentially remains unpolarized. However, when linear or plane polarized electromagnetic radiation, such as light, is incident upon a polished metallic surface, the orientation of the propagating wave motion is generally transformed from a rectilinear to an elliptic one, and the light becomes elliptically polarized.
As indicated above, a single polarizing filter polarizes up to a maximum of half the intensity of unpolarized electromagnetic radiation, and, depending upon the relative angular orientation of the polarizing planes of two polarizing filters placed in series, transmission of electromagnetic radiation, initially unpolarized when directed into the first polarizing filter, successively passing through the second polarizing filter can be controlled down to a minimum of zero if the double polarization is complete. Based on this phenomena, and on the absorption, scattering and reflecting mechanisms involving linear or plane polarized electromagnetic radiation, polarized components of scattered or reflected electromagnetic radiation can also be polarized by directing such polarized components into a polarizing filter, for partly or entirely removing these polarized components from the electromagnetic radiation exiting the polarizing filter, which is a powerful tool used in a variety of fields, especially in photography.
Accordingly, properly controlling position and angular orientation settings of a polarizing filter are advantageously used in a variety of applications for effectively and efficiently controlling and exploiting propagating electromagnetic radiation, in general, and linear or plane polarized components of propagating electromagnetic radiation, in particular. Especially in the field of photography, a polarizing filter attached or connected to a camera properly positioned and oriented relative to a source of electromagnetic radiation and subjects and objects being photographed, and, set at optimum or strategic polarizing angles, is used for eliminating, minimizing, or exploiting, the above described polarized components of scattered and reflected xe2x80x98interfering lightxe2x80x99, for substantially improving photographic results, by improving saturation of desirable colors, by enabling a photographer to concentrate better on important image details during focusing and imaging procedures, by enabling a photographer to use optimal exposure settings, and by enabling a photographer to utilize a variety of special artistic and creative photographic techniques and effects not possible without the presence of such polarized light.
As indicated above, the present invention is primarily directed to applications of a polarizing filter in the field of photography, accordingly, prior art teachings of controlling a polarizing filter summarized below relate to the field of photography. In photography, for dealing with the effects of xe2x80x98interfering lightxe2x80x99 caused by scattering and reflections, typically, a polarizing filter is attached or connected to the front of the camera lens barrel, the camera and the attached polarizing filter are strategically positioned relative to a light source and subjects and objects of a scene, and the polarizing filter is then manually rotated by the photographer to a particular angle for eliminating, minimizing, or exploiting, the intensity of the interfering light. There are prior art teachings of various methods and devices for manually using or controlling a polarizing filter attached to a camera.
In Japanese Patent No. JP58052606, issued to Tooru et al., there is disclosed a device attached to a photographic lens barrel, wherein a polarizing filter is manually rotated by turning a knob whose opposite end is part of a gear mechanism including a filter frame holding the polarizing filter.
In Japanese Patent No. JP10319474, issued to Tomoaki, there is disclosed a polarizing filter frame attached to a photographic lens barrel, wherein a polarizing filter is manually rotated by rotating a polarizing filter holding frame with respect to the polarizing filter frame, such that rotation of the polarizing filter holding frame is separate from rotation of the focusing mechanism. In this disclosure, the device enables rotating and fixing the position of a polarizing filter separate from using the focusing mechanism of a camera.
In Japanese Patent No. JP11218799, issued to Kunio, there is disclosed a device attached to a camera, whereby rotating a wheel while pressing it against the outer peripheral surface of a polarizing filter, enables rotating of the polarizing filter.
The most significant limitation of each of these teachings is the necessity of manually rotating and/or adjusting the polarizing filter or polarizing filter mechanism, according to desired extent of decreasing or exploiting interfering light intensity, prior to photographing a scene. The photographic process becomes quite cumbersome when there is a need for manually rotating and properly adjusting the polarizing filter for attempting to achieve optimum results in addition to the simultaneous need for focusing subjects and objects of a scene to be photographed. Clearly, this limitation is even more pronounced for a photographer using a photographic xe2x80x98panningxe2x80x99 technique, whereby a camera is discontinuously or continuously panned or rotated about an axis of rotation of the camera in a horizontal plane, while photographing different fields of view of the scene. This important limitation affects novice as well as professional photographers.
Overcoming the described limitation of having to manually rotate and/or adjust the polarizing filter or polarizing filter mechanism during the photographic process is addressed in U.S. Pat. No. 6,028,303, issued to Suzuki. There is disclosed a polarizing filter control mechanism used in a camera that automatically rotates a polarizing filter in order to minimize the effects of reflected light on a photographic image. An imaging element, positioned on the camera head of a camera, obtains an image signal proportional to the intensity of reflected light entering the camera lens. The image signal is electrically converted into a level detection signal which is sent to a minimum value detection unit, whereby the level detection signal is compared to a reference signal for producing a corresponding error signal. A drive control unit rotates the polarizing filter until the difference between the level detection signal and the reference signal is minimized. A significant limitation of this device is the need for designing and using relatively sophisticated, and probably costly, electronics and optics for the imaging element and associated components of the device. Another limitation is the uncertainty involved with respect to applying the invention to different types of cameras.
To one of ordinary skill in the art, there is thus a need for, and it would be useful to have a method and device for automatically controlling a polarizing filter. Moreover, there is a need for such a method and device capable of automatically sensing, measuring, and analyzing at least one parameter associated with direction of a polarizing filter by an electronic direction/motion sensing mechanism, for automatically actuating a polarizing filter rotating mechanism which automatically rotates the polarizing filter. Furthermore, there is a need for such a method and device which are relatively simple and inexpensive to implement, and which are generally applicable in the field of photography and in a variety of other fields involving the use of polarized electromagnetic radiation for viewing, imaging and/or projecting through short or long distances, for example, involving the use of a microscope, binoculars, a telescope, or a laser beam device.
The present invention relates to a method and device for automatically controlling a polarizing filter. In general, the invention features automatically sensing, measuring, and analyzing at least one parameter associated with direction of a polarizing filter by an electronic direction/motion sensing mechanism, receiving a signal from the electronic direction/motion sensing mechanism relating to the at least one parameter associated with direction of the polarizing filter by a rotation control circuit, and receiving a signal from the rotation control circuit relating to the at least one parameter associated with direction of the polarizing filter by a polarizing filter rotating mechanism for automatically rotating the polarizing filter. In particular, the invention features an electronic direction/motion sensing mechanism automatically sensing and measuring the amount of horizontal shift in the direction of the polarizing filter when an electromagnetic radiation receiver, such as a camera or an object exposed to a laser beam, hosting the polarizing filter, rotates around one of its vertical axes, such as by panning a camera, and converts the measured amount of shift into a signal for automatically actuating a polarizing filter rotating mechanism which automatically rotates the polarizing filter around its optical axis.
Thus, according to the present invention, there is provided a method for automatically controlling a polarizing filter, the method comprising the steps of: (a) sensing, measuring, and analyzing at least one parameter associated with direction of the polarizing filter by an electronic direction/motion sensing mechanism; (b) receiving a signal from the electronic direction/motion sensing mechanism relating to the at least one parameter associated with direction of the polarizing filter by a rotation control circuit; and (c) receiving a signal from the rotation control circuit relating to the at least one parameter associated with direction of the polarizing filter by a polarizing filter rotating mechanism for automatically rotating the polarizing filter.
According to another aspect of the present invention, there is provided a device for automatically controlling a polarizing filter, comprising: (a) an electronic direction/motion sensing mechanism for sensing, measuring, and analyzing at least one parameter associated with direction of the polarizing filter; (b) a rotation control circuit for receiving a signal from the electronic direction/motion sensing mechanism relating to the at least one parameter associated with direction of the polarizing filter; and (c) a polarizing filter rotating mechanism for receiving a signal from the rotation control circuit relating to the at least one parameter associated with direction of the polarizing filter for automatically rotating the polarizing filter.
According to another aspect of the present invention, there is provided a device for automatically controlling a polarizing filter associated with an electromagnetic radiation receiver, the polarizing filter polarizes electromagnetic radiation propagating into the polarizing filter for forming polarized electromagnetic radiation received by the electromagnetic radiation receiver, the device comprising: (a) an electronic direction/motion sensing mechanism for sensing, measuring, and analyzing at least one parameter associated with direction of the polarizing filter; (b) a rotation control circuit for receiving a signal from the electronic direction/motion sensing mechanism relating to the at least one parameter associated with direction of the polarizing filter; and (c) a polarizing filter rotating mechanism for receiving a signal from the rotation control circuit relating to the at least one parameter associated with direction of the polarizing filter for automatically rotating the polarizing filter associated with the electromagnetic radiation receiver.
According to another aspect of the present invention, there is provided a device for automatically controlling a polarizing filter associated with a photographic device, the polarizing filter polarizes electromagnetic radiation propagating into the polarizing filter for forming polarized electromagnetic radiation received by the photographic device, the device comprising: (a) an electronic direction/motion sensing mechanism for sensing, measuring, and analyzing at least one parameter associated with direction of the polarizing filter; (b) a rotation control circuit for receiving a signal from the electronic direction/motion sensing mechanism relating to the at least one parameter associated with direction of the polarizing filter; and (c) a polarizing filter rotating mechanism for receiving a signal from the rotation control circuit relating to the at least one parameter associated with direction of the polarizing filter for automatically rotating the polarizing filter associated with the photographic device.
According to another aspect of the present invention, there is provided a device for automatically controlling a polarizing filter associated with a laser beam device, the polarizing filter polarizes electromagnetic radiation generated by the laser beam device for forming polarized laser beam electromagnetic radiation, the device comprising: (a) an electronic direction/motion sensing mechanism for sensing, measuring, and analyzing at least one parameter associated with direction of the polarizing filter; (b) a rotation control circuit for receiving a signal from the electronic direction/motion sensing mechanism relating to the at least one parameter associated with direction of the polarizing filter; and (c) a polarizing filter rotating mechanism for receiving a signal from the rotation control circuit relating to the at least one parameter associated with direction of the polarizing filter for automatically rotating the polarizing filter associated with the laser beam device.
According to another aspect of the present invention, there is provided a method for automatically controlling a polarizing filter, the polarizing filter polarizes electromagnetic radiation propagating into the polarizing filter for forming polarized electromagnetic radiation received by an electromagnetic radiation receiver, the method comprising the steps of: (a) sensing, measuring, and analyzing at least one parameter relating to a shift in direction of the polarizing filter caused by rotating the electromagnetic radiation receiver around an axis of rotation of the electromagnetic radiation receiver, by an electronic direction/motion sensing mechanism, for generating an electronic signal relating to the shift, where the electronic direction/motion sensing mechanism is physically connected and fixed to the electromagnetic radiation receiver; (b) receiving the electronic signal from the electronic direction/motion sensing mechanism relating to the shift in the direction of the polarizing filter, by a rotation control circuit, for generating a control signal relating to angular positions and rotation of the polarizing filter; and (c) receiving the control signal from the rotation control circuit by a polarizing filter rotating mechanism for automatically rotating the polarizing filter around an optical axis of the polarizing filter to a pre-determined angular position.
According to another aspect of the present invention, there is provided a device for automatically controlling a polarizing filter, the polarizing filter polarizes electromagnetic radiation passing through the polarizing filter for forming polarized electromagnetic radiation received by an electromagnetic radiation receiver, comprising: (a) a polarizing filter frame for holding the polarizing filter, where the polarizing filter frame is connected and fixed to the electromagnetic radiation receiver; (b) an electronic direction/motion sensing mechanism for sensing, measuring, and analyzing at least one parameter relating to a shift in direction of the polarizing filter caused by rotating the electromagnetic radiation receiver around an axis of rotation of the electromagnetic radiation receiver, and for generating an electronic signal relating to the shift, where the electronic direction/motion sensing mechanism is connected and fixed to the electromagnetic radiation receiver; (c) connecting and fixing elements for connecting and fixing the polarizing filter frame and the electronic direction/motion sensing mechanism to the electromagnetic radiation receiver; (d) a rotation control circuit for receiving the electronic signal from the electronic direction/motion sensing mechanism relating to the shift in the direction of the polarizing filter, and for generating a control signal relating to angular positions and rotation of the polarizing filter within the polarizing filter frame; and (e) a polarizing filter rotating mechanism for receiving the control signal from the rotation control circuit, for automatically rotating the polarizing filter around an optical axis of the polarizing filter to a pre-determined angular position.
The method and device of the present invention serve as significant improvements over currently used techniques for controlling a polarizing filter used in a variety of fields such as physics, materials science, optics, and photography. The present invention is generally applicable to essentially any type of electromagnetic radiation receiver, such as a camera, and is relatively simple and inexpensive to implement.